A stamper has ever been used for reproducing a large amount of an optical disk represented by CD (Compact Disc), DVD (Digital Versatile Disc) and the like. There is formed on the surface of the stamper convex-concave pattern corresponding to pits and grooves to be formed on the optical disk, such as CD, DVD and the like. An optical disk substrate having same convex-concave pattern can be mass produced by an injection molding of a resin material as a substrate for the optical disk onto said convex-concave pattern of the stamper.
As for a material for forming above-mentioned stamper, nickel, copper and silver have been used due to good molding performance thereof.
However, in case that a large amount of the optical disk substrate was reproduced by using the stamper made of material such as nickel and the like, such problem sometimes occurred that a part of the stamper contacting with the resin material (this part of the stamper is hereinafter called “stamper surface” in some cases) was subject to corrosion according to chlorine component and the like contained in the resin material used for the optical disk substrate, and therefore, the correct reproduction of prescribed pits could not be achieved precisely along with a progress of the corrosion after repeating the reproduction many times.
In particular, when a polycarbonate resin was used as the resin material for the optical disk substrate because it was relatively cheap, the problem became more serious since in some cases a large amount of chlorine component was contained as an impurity in said resin material.
The present invention has been made with consideration of these problems. One of the objectives to be achieved by the invention is to provide with a stamper having excellent durability in use without causing corrosion on a part of the stamper contacting with a resin material even when a large amount of an optical disk substrate is reproduced, and also, to provide with a method by which the stamper can be manufactured efficiently.